SharePoint has a machine translation service that can be used to translate certain documents and phrases. Out of the box, it can be used by Variations to translate pages, and by the Managed Metadata Service to translate terms in the term stores. Beyond that, it is available through the API, and PointFire products make use of it.

For the past several months, Microsoft has been introducing a far superior machine translation engine. So far it is available in English, French, Arabic, Chinese simplified (Mandarin), German, Italian, Japanese, Korean, Portuguese, Russian, and Spanish.

It is not automatically used unless you specifically configure the machine translation service for it. Simply open a session in the SharePoint Management Shell and issue this commandlet:

That's it! In this case the service was named "Machine Translation Service". For examples of the old vs the new engine, see http://translate.ai

SharePoint Online uses the old engine, and there is nothing you can do about it. I don't think you can configure the machine translation service for your tenant. Maybe you can request it nicely or vote it up.

In addition to the well-known language settings that were discussed in an earlier post, there is a little-known language setting with a different set of advantages and disadvantages. We call it User Properties. To get to it, add "_layouts/15/regionalsetng.aspx?Type=user" to a web site URL in SharePoint Online or on 2013 or 2016. You will see this familiar but subtly different page:

It's quite similar to the User Profile pages, but with some differences, some good and some bad.

Advantages:

The effect of a language change here are immediate. There is no message saying that the changes may take some time to take effect.

You do not need to have counter-intuitive settings for your user profile and your Office 365 user settings like we do for the instant toggle trick.

Disadvantages:

The setting is site collection specific. On other site collections, your previous user profile settings still apply

The setting page is usually not reachable through the menus, and some parts of it do not work.

While changing your user profile will also change your user properties, the reverse is not true.

Some software will still follow your user profile settings rather than your user properties.

The setting is not synchronized with Active Directory.

Once the user profile and user properties are no longer in sync, it is difficult to get the user profile to work correctly again.

How does it work:

What sets the user profile is the User Setting Provider. Every web application has a User Settings Provider. By default it's the User Profile User Settings Provider, and that's always the one used on SharePoint Online. When you change your user profile, it's using the User Profile User Settings Provider. However if you set up your web application with no User Settings Provider, then the personal menu takes you to _layouts/15/regionalsetng.aspx screen rather than to the user profile screen.

After the User Profile Settings Provider has changed its language setting, a timer job will periodically copy the profile setting to the user properties of all site collections. This timer job typically runs once every minute, hence the delay between changing your language setting in your profile and having that setting take effect.

When you change your Office 365 account language setting, that new setting propagates in two major steps. First it copies itself to the User Profile's Display Language setting, then up to a minute later the user profile setting is copied to the user properties of all the sites. This includes MySite, which is what controls the language settings of the OneDrive for Business accounts.

If you are using PointFire on premise, PointFire's language setting mechanism overrides all three SharePoint language settings, so none of this has any effect, but for PointFire 365, PointFire's language toggle sets the SharePoint Online language settings, it does not override them.